This invention relates to methods for the prevention of the adhesion of bacterial cells to surfaces in aqueous systems by treating the water in contact with such surfaces with very low concentrations of a water-soluble ionene polymer. More particularly, it relates to methods for controlling the biological fouling of such surfaces by inhibiting the formation of a bacterial biofilm that is the common precursor to such fouling.
Biological fouling of surfaces is a serious economic problem in many commercial and industrial aqueous processes and water-handling systems. The fouling is caused by the buildup of microorganisms, macroorganisms, extracellular substances, and dirt and debris that become trapped in the biomass. The organisms involved include bacteria, fungi, yeasts, algae, diatoms, protozoa, macroalgae, barnacles, and small mollusks like Asiatic clams. If not controlled, the biofouling caused by these organisms can interfere with process operations, lower the efficiency of processes, waste energy, and reduce product quality.
For example, cooling water systems used in power-generating plants, refineries, chemical plants, air-conditioning systems, and other commercial and industrial operations frequently encounter biofouling problems. Such water systems are commonly contaminated with airborne organisms entrained from cooling towers as well as waterborne organisms from the system's makeup water supply. The water in such systems is generally an excellent growth medium for these organisms, with aerobic and heliotropic organisms flourishing on the towers and other organisms colonizing and growing in such areas as the tower sump, pipelines, heat exchangers, etc. If not controlled, the biofouling resulting from such growth can plug the towers, block pipelines, and coat heat-transfer surfaces with layers of slime, and thereby prevent proper operation and reduce cooling efficiency.
Industrial processes subject to problems with biofouling include those used for the manufacture of pulp, paper, paperboard, and textiles, particularly water-laid nonwoven textiles. For example, paper machines handle very large volumes of water in recirculating systems called "white water systems." The furnish to a paper machine typically contains only about 0.5% of fibrous and nonfibrous papermaking solids, which means that for each ton of paper almost 200 tons of water pass through the headbox, most of it being recirculated in the white water system.
These water systems provide excellent growth media for microorganisms, which can result in the formation of microbial slime in headboxes, waterlines, and papermaking equipment. Such slime masses not only can interfere with water and stock flows, but when they break loose they can cause spots, holes, and bad odors in the paper as well as web breaks that cause costly disruptions in paper machine operations.
To control biological fouling, it has been common in the art to treat the affected water systems with certain chemical substances in concentrations sufficient to kill or greatly inhibit the growth of the causative organisms. For example, chlorine gas and hypochlorite solutions made with the gas have long been added to water systems to kill or inhibit the growth of bacteria, fungi, algae, and other troublesome organisms. However, chlorine compounds are not only damaging to materials of construction, they also react with organics to form undesirable substances in effluent streams, such as carcinogenic chloromethanes and chlorinated dioxins.
Certain organic compounds, such as methylenebis(thiocyanate), dithiocarbamates, haloorganics, and quaternary ammonium surfactants, have also been used. While many of these are quite efficient in killing microorganisms or inhibiting their growth, they also tend to be toxic or harmful to humans, animals, or other non-target organisms.
Scientific studies have shown that the first stage of biological fouling in aqueous systems is generally the formation of a thin bacterial film on the surface exposed to the water. The bacteria initiate the attachment and early colonization of the surface and modify it in a manner that favors the development of the more complex community of organisms that make up the advanced fouling of the surface. For example, P. E. Holmes (Appl. Environ. Microbiol. 52(6):1391-3, Dec. 1986) found that bacterial growth on the submerged surfaces of vinyl swimming pool liners was a significant factor in the fouling of these surfaces by algae. When in association, the bacteria attached to the vinyl within 24 hours and the algae within 48 hours. In the absence of bacteria, however, one species of algae did not attach even after 7 days and another algae species did begin to attach by 7 days but in numbers a order of magnitude lower than those of the bacteria-contaminated counterpart. A general review of the mechanisms of biological fouling and the importance of the bacterial biofilm as the initial stage is given by C. A. Kent in "Biological Fouling: Basic Science and Models" (in Melo, L. F., Bott, T. R., Bernardo, C. A. (eds.), Fouling Science and Technology, NATO ASI Series, Series E, Applied Sciences: No. 145, Kluwer Acad. Publishers, Dordrecht, The Netherlands, 1988).
Based on these findings, one possible way to control the biological fouling of surfaces would be to prevent or inhibit the formation of the initial bacterial biofilm. This can be done, of course, by use of bactericidal substances, but they generally have the disadvantages mentioned above. It is therefore an object of the present invention to provide a method of controlling the biological fouling of surfaces that obviates the disadvantages of the prior art. Other objects and advantages of this invention will become apparent from a reading of the specifications and appended claims.